Optical Coherence Tomography (OCT) is a technique for imaging into samples, such as tissue, glass and the like. Recent advances in OCT have increased the imaging speed, allowing large image sets, such as three dimensional volumes, to be generated relatively quickly. As OCT is typically high-speed, non-contact and non-destructive, it may be useful for imaging dynamics over short time scales, for example, well below 1.0 second, such as the beating of a heart tube in a fruit fly, and for imaging physiological changes that occur over a long time scales, for example, over days or even longer, such as over the time it takes tissues to develop or to respond to interventions.
A variety of approaches to imaging using OCT are known. Such systems may be characterized as Fourier domain OCT (FD-OCT) and time domain OCT (TD-OCT). FD-OCT generally includes swept source (SS) and spectral domain (SD), where SD systems generally use a broadband source in conjunction with a spectrometer rather than a swept laser source and a photodiode(s). TD systems generally rely on movement of a mirror or reference source over time to control imaging depth by providing coherence depth gating for the photons returning from the sample being imaged. Each system uses broadband optical sources, producing a low effective coherence that dictates the achievable resolution in the depth, or axial, direction.
These imaging techniques are derived from the general field of Optical Low Coherence Reflectometry (OLCR); the time domain techniques are derived from Optical Coherence Domain Reflectometry, swept source techniques are derived from Optical Frequency Domain Reflectometry, and spectral domain techniques have been referred to as “spectral radar.”
In contrast to time domain systems, in FD-OCT the imaging depth may be determined by Fourier transform relationships between the acquired spectrum, rather than by the range of a physically scanned mirror, thereby allowing concurrent acquisition of photons from all imaged depths in the sample. Specifically, in FD-OCT, the optical frequency interval between sampled elements of the spectrum may be used to control the imaging depth, with a narrower sampling interval providing a deeper imaging capability.
The use of OCT to make accurate, quantitative measurements over time, may be difficult due to the challenge of ensuring, among other things, that measurements made at different times are taken from the same place in the sample.
With the advent of FD-OCT techniques, it becomes possible to generate practical 3D images, and from these 3D images a planar en-face image. One technique for generating an en-face view and correlating depth-resolved features with landmarks observed on this en-face view are discussed in Simultaneous acquisition of sectional and fundus ophthalmic images with spectral-domain optical coherence tomography by Jiao et al. (24 Jan. 2005/Vol. 13, No. 2/OPTICS EXPRESS 445), the content of which is hereby incorporated herein by reference as if set forth in its entirety.